1. Field of the Invention
This invention relates to a cogeneration system, particularly to a cogeneration system responsive to a commercial power network outage for supplying a load with as much electric power as possible.
2. Description of the Related Art
In recent years, cogeneration systems have been developed that are equipped with an internal combustion engine-driven generator for installation in an AC power supply line between a commercial power network and an electrical load for supplying power to the load in interconnection with the power network and also for supplying hot water or air or the like heated using exhaust heat from the engine to a thermal load. Such a cogeneration system is taught, for example, by Japanese Laid-Open Patent Application No. Hei 5 (1993)-328615.
In the cogeneration system taught in the reference, an engine-operated, on-site power generation plant is connected to an on-site load and three other loads are connected to be switchable between a commercial power utility (commercial power network) and the engine-operated, on-site power generation plant. When the operating load of the on-site load exceeds a predetermined value, the other three loads are connected to the commercial power utility side and as the amount of operating load decreases below the predetermined value, the other three loads are sequentially connected to the engine-operated, on-site power generation plant.
When the power network interconnected with this type of cogeneration system experiences an outage, the ordinary practice is to shut down the cogeneration system to prevent a reverse flow of its power output into the power network. Alternatively, it is conceivable to not shut down the cogeneration system at the time of a power failure but to keep it operating for supplying power to the electrical load. In this case, however, the maximum amount of power that can be supplied is limited to the inherent maximum output of the cogeneration system.